How does a Phantom Grip Limited Slip insert REALLY work?

How does a Phantom Grip Limited Slip insert REALLY work?

For a while now, I have been wondering how a Phantom Grip Limited Slip open differential conversion works. I have read often enough on Honda-Tech.com about how “Phantom Grip LSD’s don’t work” or “cause excessive metal shavings in the transmission oil”, and other horror stories. Never the less, lots of people are lured into buying them because “they are so much cheaper than a normal LSD”. Well, after reading this post on Honda-Tech, I decided to write this entry to study the problem and document the thought process. Hopefully you will understand the fundamentals of how a Phantom Grip Limited Slip insert works by the end of this article, and will be able to decide for yourself whether it is worth the money.

For this explanation to work, it helps to have some insight into how an LSD mystery box works. In this case, we will discuss a clutch-type LSD since this is the style of LSD the Phantom Grip purports to be closest to. But first, a picture for reference:

Diagram 1: This is a basic layout image of a FWD Clutch Type LSD
Diagram 1: This is a basic layout image of a FWD Clutch Type LSD


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A Clutch-Type Limited slip differential works by using a high friction clamping surface(orange in color), sometimes many plates with high friction surfaces, to resist independent motion of the gears fixed to the axles(in green), and thus causes the front wheels to spin at the same speed. This independent motion can be caused by driving through a corner, where the outside wheel spins faster than the inside wheel, or often also by torque steer. If you go into a hard left corner, the left side axle (in black, attached to the green) will be spinning slow with not very much load on it, and the right side will be spinning faster with lots of load on it. This causes the clutch friction material on the left side to break free and rotate the pressure ring gear on the left side at the same rate as the pressure ring gear on the right side, but since the gear fixed to the axle on the left side is not attached directly to the pressure ring gear on the left, it simply overcomes the friction material’s resistance, and is allowed to spin.

Torque steer is particularly common in front wheel drive cars, where one drive axle is longer than the other, causing different amounts of torque to be applied to each wheel. This high friction surface still allows the wheels to turn independently of each other, but is not nearly as willing to allow this because the high clamping force imparted on the friction surface by the internal springs (baby blue color) of the differential. This willingness to spin both sides at different rates in the clutch type differential is significantly less than the willingness to allow both sides to spin at a different rate that an open differential normally allows.  The consequence is that if you do a burnout in a open differential car, and turn the wheel slightly, you may end up with one wheel of fury, while the other wheel is just hanging out. The clutch type differential can help greatly in using the traction of both tires during a burnout, even at a higher than 0 degree steering angle, and it is all thanks to the calibration of the clutch friction material and the pressure exerted on the pressure ring gears by the clutch pressure ring springs.

Careful engineering is performed to find a good balance between friction surface area and spring strength, so the differential is not locked all the time, but not so weak that it acts as an open differential.

Next, a diagram of a stock Honda FWD differential with the “Phantom Grip Limited Slip” insert:

Diagram 2: This is what a Phantom Grip Limited Slip insert in a Stock Honda FWD "open" Differential looks like.
Diagram 2: This is what a Phantom Grip Limited Slip insert in a Stock Honda FWD "open" Differential looks like.

As you can see from the diagrams, right off the bat, calling a Phantom Grip insert a clutch type differential is not entirely true, because there is no clutch friction material(orange in color, diagram 1) as there is in a normal clutch type differential. In fact, there are several parts that appear absent in comparing diagrams 1 and 2.

You may also note that the clutch type LSD has pressure ring gears (brown in color, diagram 1) driven by the planetary gear system(purple in color, diagrams 1 and 2), where as the Phantom Grip planetary gears are simply the planetary gears provided by the OEM manufacturer of the open diff.

This brings the next question: If the Phantom Grip has no clutch friction material, and the pressure ring component is  a gear already being driven directly by the planetary gear system, then how does it work?

It appears that the Phantom Grip Limited Slip insert is only capable of providing friction on the gears driving the axles, which attempts to keep the wheels moving at the same speed.  It is important to note that the springs (baby blue in color) in both diagrams are providing some large force  in the direction of the gears connected to the axles. In a normal clutch type differential, this force increases the clamping force of the clutch plates much in the same way as a higher clamping load clutch helps a high horsepower car’s clutch not slip when the clutch is dumped. The Phantom Grip Limited Slip insert is imparting force via a spring in the same manner, but that clamping force is being exerted on the gear hub and the face of the axle gears! There is no friction material, and no set of flat side gears for a friction surface at all. In fact the total friction surface area provided by the stock open diff, all together,  is probably less than 1 inch square. Unless the springs in the device provide tens of  thousands of psi of force, it is unlikely that this device would do anything at all.  This is astonishing!  A quick look at an installed Phantom Grip Limited Slip insert shows how small the axle gear to limited slip insert contact surface must be.


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Phantom Grip Installation Contact area
Diagram 3: As you can see in this picture, the top and bottom of the metal box (Phantom Grip Limited Slip insert) in the hands of the installer will impart friction on the internal axle side gears of the open differential.

Diagram 3 above makes a big case for what shows up below. You notice that in the gears that are attached to the axle, the gears are sloped downward, while the Phantom Grip plate is flat. You will also note that the contact patch is a steel gear to aluminum or steel Phantom Grip plate contact, which when covered in transmission oil, can’t possible impart that much friction on the axle gears, even with monster springs.

In the following picture, Diagram 4, you can see that the theoretical surface area of contact for the Phantom Grip limited slip insert on the tapered gear that is fixed to the axle in green is miniscule. The drawing below is not to scale in any sort of way, so the angle of contact may be more or less shallow, but it illustrates just how much different the Phantom Grip Limited Slip insert is from a real Clutch Type limited slip.

Diagram 4: Theoretical side view of the Phantom Grip contact plate to axle gear
Diagram 4: Theoretical side view of the Phantom Grip contact plate to axle gear

It may now be obvious how metal shavings will most likely wind up in your oil using the Phantom Grip. The friction plate of the device itself is resting on gears that don’t necessarily spin incredibly fast or for long periods of time, but they do spin, and over time, it is easy to see how the friction plate of the Phantom Grip may be worn down due to the tiny contact patch and heavy load on that patch. Real clutch type LSD’s have wearing issues of their own, but are engineered from the beginning for the purpose of acting as a clutch.

So with that, we come to the end of this post. A few unknowns are left for me to ponder, such as the actual, real contact area the Phantom grip has in a normal Honda open diff, and also what exactly the spring pressure is in the limited slip insert. These factors can make a difference in how well the device works, but in my opinion, this short explanation is enough for me to determine that I will absolutely spend the extra $400 or $500 for a real clutch type or helical LSD over the Phantom Grip Limited Slip insert.



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  • Mick

    Thanks for the write up!

  • Thomas

    All that write up and you didn't even try it? What about the actual seat of the pants opinion? Phantom Grip does not claim to be a clutch type limited slip. This is what others have compared them too.

    Your article falls short of actual use although you have a lot of personal theory. Did you not get a free sponsorship from them or something?

  • Jon

    My write-up is an engineering theory study. I see kits purporting to be an LSD conversion for an open diff, and they contain 2 plates and some springs and is half the price of an OBX or a quarter the price of a quaife. All that gives me is a lot of questions. No extra gears, no clutch pack, no obvious means of performing that duty. Makes you wonder why OEM's don't buy the Phantom Grip and put it in their cars if it works so well and adds so little cost.

    All I can do is provide the information and point out noticeable deficiencies in design, which is what I think I have done.

    I would be happy to take a product sample and try it out, and I have no reason to be sponsored for anything, so I have no quarrel with the company.

    I can provide references to several people who can better answer your question in terms of actual use. They are available via private message on Honda-tech.com under the usernames Bense, or Aquafina and on d-series.org under the username transzex or Aquafina(same guy).

    All 3 guys listed are honda transmission gurus and will undoubtedly tell you from experience what is up, if you don't believe or understand the evidence I have presented here on the topic.

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  • Myles

    This is an excellent write up, I had no idea that this was how the Phantom LSD conversion worked. There is not a chance I will be buying one.

    How could metal vs metal with differential oil act as a frictional material in an adequate manner? I don’t think it could.

  • Ferp420

    you are missing the alot in your write up the springs dont create the lock up force the drag from the gears create pull on the insert causing them to be forced apart by the cross pin witch in turn locks the diff creating all that hundreds of pounds of force you where talking about  if its a race car and gets rebuilt alot im sure it would be ok or used  in the rear end of say a subaru with part time 4wd where it would spend most of its time freewheeling and have no torque applied to it but even then it will where out and the carriers arent built for that kind of force to be applied to them it dose have its advanteges and disadvantages i would not run one inside a trans but in a rear diff why not 

  • TBM

    While I appreciate the in-depth view at the PG LS insert from a theoretical perspective, particularly with regards to the Honda transmission issues, what’s lacking is a comprehensive understanding, view and consideration of engineering vector and torque force concepts. A differential has multiple forces and directions of those forces (i.e. vectors). Each combination results in a different counter force and resulting vector.

    First off, to suggest that frictional forces effectively become zero simply because of the presence of oil between two components is a complete and total lack of understanding of forces and materials. If friction completely vanished when two objects [attempt to] make contact, oils wouldn’t A) need to come in various viscosities B) wouldn’t heat up and then lead to C) break down. Oil is a fluid that has varying degree of compression. Oil between two objects moving in 180 degree opposite directions provide a ‘slippery’ [practically friction less] interaction. However, oil between two objects moving along the same vector (force + direction) will simple compress to a level at which point it becomes essentially a solid….think hydro locking one’s engine. (i.e. water in your combustion chamber).

    With that said, one has to understand and consider that when two wheels on an axis of a differential are going at different rates of rotation, the center pinion begins to rotate. Let’s look closer at this rotation. This rotation is the result left and right axes spider gears essentially attempting to push themselves off and away (180 degrees from one another) from the center pinion spider gears.

    However, because these components are mechanically forced to remain in place [thanks to carrier, thrust washers, bearings, etc] they do not substantially push far away. But make no mistake there are extreme outward (parallel to ground-perpendicular to wheel center hub) forces pressing the spider gears against the carrier. Ever see the slow motion of how a golf ball compresses at the moment of impact with a golf club? They don’t make a carrier out of cast iron for nothing. However, in an open differential design, the softer material of the thrust washers, viscosity and compression of the oil, and play in the gears all give a bit of ‘play’ to allow the spider gears enough ‘breathing room’ to rotate freely .

    BUT if you add a PG like device that simply generates additional outward compression forces [to increase the friction that the thrust washer, et al, cannot compensate for], voila, you now how a temporarily ‘locked’ differential…until the rotational forces overcome friction of the compression from the springs. The key then is to find the right spring pressures for one’s particular housing, engine output, vehicle weight and, of course, washer/gear friction and strength.

    That said, I think a more likely reason for the metal shavings within Honda transmissions that use this product are not necessarily the ‘quality’ of the product but rather strength of the individual Honda transmission components. Honda engineers designed their transmissions to operate in an open differential design in a light weight vehicle with low torque output engines. That means extensive use of lightweight, thin, and/or soft bearing, gears and washers. Therefore, it should be of very little surprise to ANYONE that when you add additional compression forces against such components AND remarkably increase the torque output of an engine…well…said components shear, shatter, and every other conceivable form of metallic destruction…oil or no oil. Hence, transmission and differentials of heavier, beefier construction and vehicles don’t have the high rate of failure (if any) that the Honda’s are seemingly notorious for.

    The take away. Insure the differential housing support components are up to snuff before using said product.

  • Luca

    All clutch lsd have metal plates rotating. They produce metal shavings. They work with 75w-90 transmission oil. All they win races. Don’t know PG. PG is easy: spyder gears slip against cause of two plates with springs. Maybe if they decide to buy lsd they can try PG with stock diff before.
    Torsen, Quaife, LSD, PG they are all different, they work different, not everybody drive same way, not only road, nor race only. I don’t know PG. Only I read who tried is happy.
    Who did not try say it bad. Curious.

  • Tiago Beltrão

    Excellent article! Very well explained.

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